Preferred compositions employed heretofore for binding sand in forming foundry cores or molds have included water-producing condensation reaction products, addition reaction products of at least two components, or time-consuming oxidative polymerizations. These reactions have in practice been carried out with the familiar phenol-, furan- or phenol-isocyanate, urea-formaldehyde resins and core oils.
Examples of condensation reactions in which monomeric and/or oligomeric furfuryl alcohol are employed as binders or as a binder ingredient in which the binder is hardened or set at room temperature in forming foundry cores or molds in the presence of acids are found in Swiss Pat. No. 451,413, in U.S. Pat. No. 3,145,438, in German Publication Patent No. 1,190,144, and in the British Pat. No. 832,999. Examples of acids used in those processes are: Volatile acids, HCl and as nonvolatile acids, H.sub.3 PO.sub.4.
A characteristic of the process of Swiss Pat. No. 451,413 is the use of a water solution of the acid hardening agent for the binder, which water solution as initially charged is of insufficient concentration to trigger a quick setting of the binder. Water is evaporated by passing air through the solution and the acid concentration increases to the point where setting of the binder is initiated. The water is not an inhibitor in such a process, it is a mere diluent for the acid.
British Pat. No. 768,887 describes a process for hardening or curing of thermosetting foundry binders wherein a mixture of furfuryl alcohol and maleic acid anhydride containing an ammonium chloride additive is caused to react. The ammonium chloride has the function of a latent curing catalyst or precursor, in that at elevated temperatures it will decompose to NH.sub.3 and HCl and the latter then acts as a curing catalyst.
Also, there are binders for foundry cores or molds based on water-soluble polymeric acrylates and methacrylates and/or polyacrylonitrile (See the discussion in Chemisches Zentralblatt 1961 -- chemical review, page 12, 988; Swedish Pat. No. 155,354; German Application Pat. No. 1,164,604; German Pat. No. 880,388). These all involve preformed polymerisates wherein the setting or hardening of the binder mixed with foundry sand takes place slowly as the water evaporates. The evaporation of the water requires a relatively long time resulting in correspondingly long setting times.